Start implementing pub object model. Rudimentary package cache class, and a simple pub command to l…

utils/pub/cache.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/**
+ * The local cache of previously installed packages.
+ */
+class PackageCache {
+  /**
+   * The root directory where this package cache is located.
+   */
+  final String rootDir;
+
+  // TODO(rnystrom): When packages are versioned, String here and elsewhere will
+  // become a name/version/(source?) tuple.
+  final Map<String, Package> _loadedPackages;
+
+  /**
+   * Packages which are currently being asynchronously loaded.
+   */
+  final Map<String, Future<Package>> _pendingPackages;
+
+  /**
+   * Creates a new package cache which is backed by the given directory on the
+   * user's file system.
+   */
+  PackageCache(this.rootDir)
+  : _loadedPackages = <Package>{},
+    _pendingPackages = <Future<Package>>{};
+
+  /**
+   * Loads all of the packages in the cache and returns them.
+   */
+  Future<List<Package>> listAll() {
+    return listDir(rootDir).chain((paths) {
+      final packages = paths.map((path) => find(basename(path)));
+      return Futures.wait(packages);
+    });
+  }
+
+  /**
+   * Loads the package named [name] from this cache, if present.
+   */
+  // TODO(rnystrom): What happens if the package isn't cached?
+  Future<Package> find(String name) {
+    // Use the previously loaded one.
+    final package = _loadedPackages[name];
+    if (package != null) {
+      return new Future.immediate(package);
+    }
+
+    // If we are already in-progress loading it, re-use that one.
+    final pending = _pendingPackages[name];
+    if (pending != null) {
+      return pending;
+    }
+
+    return _loadPackage(name);
+  }
+
+  /**
+   * Start loading the package.
+   */
+  Future<Package> _loadPackage(String name) {
+    final completer = new Completer<Package>();
+    final pubspecPath = join(rootDir, name, 'pubspec');

[nweiz, 2012/04/17 20:08:46]

Unused variable

[Bob Nystrom, 2012/04/18 18:09:18]

Done.

+
+    _pendingPackages[name] = completer.future;
+    _parsePubspec(name).then((dependencies) {

[nweiz, 2012/04/17 20:08:46]

I think using transform here rather than manually instantiating a Completer
makes the async control flow clearer. It's also less code.

[Bob Nystrom, 2012/04/18 18:09:18]

Great idea. Still learning my way around transform() and chain().

+      final package = new Package._(this, name, dependencies);
+
+      _pendingPackages.remove(name);
+      _loadedPackages[name] = package;
+      completer.complete(package);
+    });
+
+    return completer.future;
+  }
+
+  Future<List<String>> _parsePubspec(String name) {
+    final completer = new Completer<List<String>>();
+    final pubspecPath = join(rootDir, name, 'pubspec');
+
+    // TODO(rnystrom): Handle the directory not existing.
+    // TODO(rnystrom): Error-handling.
+    final readFuture = readTextFile(pubspecPath);
+    readFuture.handleException((error) {
+      // If there is no pubspec, we implicitly treat that as a package with no
+      // dependencies.
+      // TODO(rnystrom): Distinguish file not found from other real errors.
+      completer.complete(<String>[]);
+      return true;
+    });
+
+    readFuture.then((pubspec) {

[nweiz, 2012/04/17 20:08:46]

I feel like it's a flaw in our Future API that you can't use transform here
because of the error-handling above. There should be a way of mixing transform
and handleException so you can do something like ".transformException(() =>
<String>[])".

The way it works in Closure is that onSuccess and onError both function like
#transform/#chain by default.

[Bob Nystrom, 2012/04/18 18:09:18]

Done.

+      // TODO(rnystrom): Use YAML parser when ready. For now, it's just a flat
+      // list of newline-separated strings.
+      final dependencyNames = pubspec.split('\n')
+          .map((name) => name.trim())

[nweiz, 2012/04/17 20:08:46]

I thought the style was putting the . on the previous line in the vain hope that
one day semicolons become optional.

[Bob Nystrom, 2012/04/18 18:09:18]

Done.

+          .filter((name) => (name != null) && (name != ''));
+
+      completer.complete(dependencyNames);
+    });
+
+    return completer.future;
+  }
+}